Extrusion compositions having high drawdown and substantially reduced neck-in

ABSTRACT

An ethylene polymer extrusion composition having high draw down and substantially reduced neck-in, a process for making such a composition and a process of using such a composition to prepare extrusion coatings, extrusion profiles and extrusion cast films are disclosed. The ethylene polymer extrusion composition is made of 75-95 weight percent of at least one ethylene α-olefin interpolymer and 5-25 weight percent of at least one high pressure ethylene polymer characterized as having high melt strength and a broad, bimodal molecular weight distribution. In profiles, coatings or films, the composition can be used as sealant, adhesive or abuse resistance layers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Rule 1.60 divisional of application Ser. No.08/344,262, filed Nov. 23, 1994, now U.S. Pat. No. 5,582,923, which is acontinuation-in-part application of application Ser. No. 08/327,156,filed Oct. 21, 1994, now abandoned, and a continuation-in-partapplication of application Ser. No. 08/084,054, filed Jun. 29, 1993, nowU.S. Pat. No. 5,395,471, which is a continuation-in-part application ofpatent application Ser. No. 07/776,130, filed Oct. 15, 1991, issued asU.S. Pat. No. 5,272,236; a continuation-in-part of patent applicationSer. No. 07/939,281, filed Sep. 2, 1992, issued as U.S. Pat. No.5,278,272; a continuation-in-part of application Ser. No. 08/055,063filed Apr. 28, 1993 now U.S. Pat. No. 5,562,958; and is related toapplication Ser. No. 07/961,269, filed Oct. 14, 1992, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to polyethylene extrusion compositions. Inparticular, the invention pertains to an ethylene polymer extrusioncomposition having high drawdown and substantially reduced neck-in. Theinvention also pertains to a method of making the ethylene polymerextrusion composition and a method for making an extrusion coatedarticle, an article in the form of an extrusion profile and an articlein the form of an extrusion cast film.

2. Technical Background

It is known that low density polyethylene (LDPE) made by high-pressurepolymerization of ethylene with free-radical initiators as well asheterogeneous linear low density polyethylene (LLDPE) and ultra lowdensity polyethylene (ULDPE) made by the copolymerization of ethyleneand α-olefins with Ziegler coordination (transition metal) catalysts atlow to medium pressures can be used, for example, to extrusion coatsubstrates such as paper board, to prepare extrusion cast film forapplications such as disposable diapers and food packaging and toprepare extrusion profiles such as wire and cable jacketing. However,although LDPE generally exhibits excellent extrusion processability andhigh extrusion drawdown rates, LDPE extrusion compositions lacksufficient abuse resistance and toughness for many applications. Forextrusion coating and extrusion casting purposes, efforts to improveabuse properties by providing LDPE compositions having high molecularweights (i.e., having melt index, I₂, less than about 2 g/10) are noteffective since such compositions inevitably have too much melt strengthto be successfully drawn down at high lines speeds.

While LLDPE and ULDPE extrusion compositions offer improved abuseresistance and toughness properties and MDPE (medium densitypolyethylene) extrusion compositions offer improved barrier resistance(against, for example, moisture and grease permeation), these linearethylene polymers can not be extruded or drawn down at high take-offrates and they are known to exhibit relatively poor extrusionprocessability.

The ultimate extrusion drawdown rate of ethylene α-olefin interpolymersis limited (at otherwise practicable extrusion line speeds) by the onsetof a melt flow instability phenomena known as draw resonance rather thanbeing limited by melt tension breaks due to "strain hardening" whichoccurs at higher line speeds and is typical for LDPE and other highlybranched high pressure ethylene polymers such as, for example,ethylene-acrylic acid (EAA) copolymers and ethylene vinyl acetate (EVA)copolymers.

"Draw resonance" or "melt surging" occurs in LLDPE, ULDPE and otherlinear polymers such as high density polyethylene (HDPE), polypropyleneand polyester during processing that involves rapid drawing or pullingof the melt such as extrusion coating, extrusion cast film fabrication,profile extrusion and fine denier fiber spinning. Also, the onset oroccurrence of draw resonance is unmistakable.

The patent teachings of Kurtz et al. in U.S. Pat. No. 4,339,507 andLucchesi et al. in U.S. Pat. No. 4,486,377 (the disclosures of both ofwhich are incorporated herein by reference) describe draw resonance as asustained random and/or periodic oscillation, variation or pulsation ofthe polymer melt with respect to the velocity and cross-sectional areaof a melt drawing process that occurs between the die and the take-offposition when the boundary conditions are a fixed velocity at the dieand a fixed velocity at the take-off position. Draw resonance occurswhen the draw ratio (i.e., the melt velocity at take-off divided by themelt velocity instantaneous at the die exit often approximated bydividing the reciprocal of the final polymer thickness by the reciprocalof the thickness of the melt instantaneous at the die exit) exceeds apolymer specific critical value. Draw resonance is a melt flowinstability that is manifested as irregularities in the final coating,film or fiber dimensions and often produce widely variable thicknessesand widths. When line speeds significantly exceed the speed of onset,draw resonance can cause web or filament breaks and thereby shut downthe entire drawing or converting process.

Given the various differences and intricacies that can exist betweendifferent extrusion equipment, relative resistance to draw resonance isoften expressed in terms of critical draw ratio, and for conventionallinear ethylene polymers, maximum stable draw ratios have been found tobe less than 10:1, although draw ratios greater than 20:1 are needed formost commercial drawing operations.

"Drawdown" is defined herein to mean stretching or elongating a moltenpolymer extrudate (web or filament) in the machine direction andoccasionally (simultaneously to a lesser degree) also in the transversedirection.

"Melt strength" which is also referred to in the relevant art as "melttension" is defined and quantified herein to mean the stress or force(as applied by a wind-up drum equipped with a strain cell) required todraw a molten extrudate at some specified rate above its melting pointas it passes through the die of a standard plastometer such as the onedescribed in ASTM D1238-E. Melt strength values, which are reportedherein in centi-Newtons (cN), are determined using a Gottfert Rheotensat 190° C. In general, for ethylene (α-olefin interpolymers and highpressure ethylene polymers, melt strength tends to increase withincreased molecular weight, or with broadening of the molecular weightdistribution and/or with increased melt flow ratios.

"Neck-in" which is influenced by extrudate swelling and, to lesserdegree, by surface tension effects is defined herein as the differencebetween the die width and the extrudate width at the taken-off positionor the final width of the fabricated article. Measured neck-in values(at constant output) will remain constant or decrease as the drawdownrate increases, and, in general, it is well known that for conventionalethylene polymers neck-in values increase as molecular weight decreasesand/or as the molecular weight distribution narrows. The neck-in valuesreported herein are determined at a 1 mil monolayer extrusion coatingweight using a 3.5-inch diamieter, 30:1 L/D Black-Clawson extrusioncoater equipped with a 30 inch wide die deckled to 24 inches and havinga 20-mil die gap and 50-lb. Kraft paper.

"Take-off position" is defined herein to mean the contact point (eitherthe top or bottom) of a roller device that draws or pulls the moltenextrudate down from its initial thickness instantaneous at the die exitto its final thickness. The roller device can be a nip roll, rubberroll, a chill roll, combinations thereof, or the like constructed from,for example, metal or rubber with various surfaces such as polished,matte or embossed finishes; all of which can to varying degrees affectthe onset of draw resonance.

A variety of potential solutions have been disclosed to address theneck-in and/or draw resonance tendencies of ethylene α-olefininterpolymers. Many of these solutions are equipment related and othersprimarily relate to modification of the properties of the ethyleneα-olefin interpolymer by forming a polymer blend with a highly branchedhigh pressure ethylene polymer such as, for example, low densitypolyethylene. Thompson in U.S. Pat. No. 4,348,346 (which is incorporatedherein by reference) is an example of equipment related attempts toaddress neck-in and draw resonance. Thompson describes a secondaryinjection of polymer melt streams into the primary die at the edges ofthe primary web stream is described to reduce neck-in and provideimproved edge bead control.

An equipment modification solution specific to retarding the onset ofdraw resonance is provided by Cancio et al. in U.S. Pat. No. 4,668,463and U.S. Pat. No. 4,626,574 (the disclosures of both of which areincorporated herein by reference) where locating a draw roller not morethan 6 inches (15.2 cm) from the die provides a short air/draw gap andreduced draw resonance. Luchessi et al. in U.S. Pat. No. 4,486,377,teaches the use of a fluid medium, e.g., nitrogen, carbon monoxide orair, directed against the molten web prior to the take-off position as aviable method of retarding draw resonance. Similarly, Kurtz et al. inU.S. Pat. No. 4,608,221 (the disclosure of which is incorporated hereinby reference) discloses that draw resonance can be mitigated by theutilization of a tensioning device with a friction free surface in a"rapid cooling zone" between the die and the take-off position.

Conversely, as another equipment modification example for alleviating orreducing draw resonance, Chaing in U.S. Pat. No. 4,859,379 (thedisclosure of which is incorporated herein by reference) disclosesradiant heating of the molten web prior to a chill roll take-offposition.

Examples of modified ethylene α-olefin interpolymer compositionsexhibiting reduced draw resonance include U.S. Pat. No. 4,378,451(Edwards), the disclosure of which is incorporated herein by reference,which discloses high flow rate compositions based on degraded propylenepolymers blended with low density polyethylene. A similar example isprovided by Werkman et al. in U.S. Pat. No. 3,247,290 (the disclosure ofwhich is incorporated herein by reference) wherein thermally degraded(visbroken) high density polyethylene is blended with low densitypolyethylene to prepare high drawdown extrusion coating compositions.Another ethylene α-olefin interpolymer blend example involving lowdensity polyethylene is disclosed by Kurtz et al. in U.S. Pat. No.4,339,507 where high pressure LDPE at 20 to 98 weight percent incombination with a heterogeneous conventional LLDPE is taught to provideextrusion coating compositions with improved running rates.

An example of compositions that reduce draw resonance without theinclusion of a polymer degradation step and/or blending with a branchedhigh pressure ethylene polymer is taught by Dohrer et al. in U.S. Pat.No. 4,780,264 where LLDPE with melt flow ratios less than 8.3 (i.e.,utilizing molecular weight distributions even more narrow than typicallyemployed) were found to allow surprisingly fast line speeds in extrusioncoating and extrusion casting. However, predictably, these materialsalso exhibit higher neck-in and/or poor extrusion processability (e.g.,higher extruder amperage).

In spite of the various advances, there is still a need for avoidingdraw resonance and high neck-in problems when extruding ethyleneα-olefin interpolymer compositions, particularly at high extrusion linespeeds. For example, while the compositions disclosed in co-pendingapplication Ser. No. 08/084,054, filed Jun. 29, 1993, exhibitsignificantly improved line speeds (draw-down rates), high resistance todraw resonance and reduced neck-in relative to conventional linearethylene α-olefin compositions, such compositions still exhibit highneck-in (for example, ≧7 inches at a 1.0 mil extrusion coating weight).Further, where ordinary high pressure ethylene polymers are used asblend component polymers in ethylene α-olefin polymer compositions toimproved line speed, resistance to draw resonance and neck-inperformance, relatively high concentrations (i.e., greater than 20weight percent based on the total weight of the composition) of the highpressure ethylene polymer as a blend component polymer is required toeffectuate such improvement. However, where a resin manufacturer orconverter is capacity limited, such as, for example, where the onlyavailable equipment for addition purposes is a small scale weigh-feeder,a requirement of higher concentrations of a high pressure ethylenepolymer blend component can be prohibitive.

As described hereinafter, the present invention substantially fills theneed for ethylene polymer extrusion compositions having high linespeeds, high resistance to draw resonance and substantially reducedneck-in and a method of making such compositions utilizing low capacityaddition equipment. The compositions of the present invention can beused in conjunction with known equipment modifications and incombination with thermally degraded polymers to good advantage and thecombined or synergistic benefits of the present invention and knownsolutions can also be realized.

In addition to the advantage of being able to make an improved extrusioncomposition by utilizing a wide variety of addition or blendingequipment options, converters and fabricators can now realize theadvantages of improved abuse or barrier properties (due to theutilization of ethylene α-olefin interpolymers), higher productivityrates (due to ability to obtain higher line speeds) and down-gauging(lower coat weights or thinner films and profiles), while stillpreparing high quality, uniform coatings, profiles and films. Anotheradvantage of the invention is the significantly higher melt strength ofthe inventive composition relative to unmodified ethylene/α-olefininterpolymer. This increased melt strength should allowed improved partdefinition, less sag and higher hot green strength in profile extrusionssuch as fabrication of wire and cable products.

SUMMARY OF THE INVENTION

In accordance with the present invention, we have discovered an improvedmethod of making an ethylene polymer extrusion composition, an improvedethylene polymer extrusion composition, and a method for making anextrusion coated an substrate, an extrusion profile of the ethylenepolymer composition and an extrusion cast film of the ethylene polymercomposition.

One aspect of the invention is an ethylene polymer extrusion compositioncomprising from about 75 to 95 percent, by weight of the totalcomposition, of at least one ethylene/α-olefin interpolymer compositionselected from the group consisting of a substantially linear ethylenepolymer composition, a homogeneously branched linear ethylene polymercomposition and a heterogeneously branched linear ethylene polymercomposition, wherein the ethylene/α-olefin polymer is characterized ashaving a density in the range of 0.85 g/cc to 0.940 g/cc and from about5 to 25 percent, by Weight of the total composition, of at least onehigh pressure ethylene polymer characterized as having a melt index, I₂,less than 6.0 g/10 minutes, a density of at least 0.916 g/cc, a meltstrength of at least 9 cN as determined using a Gottfert Rheotens unitat 190° C., a M_(w) /M_(n) ratio of at least 7.0 and a bimodal molecularweight distribution as determined by gel permeation chromatography,wherein the ethylene polymer extrusion composition has a melt index, I₂,of at least 1.0 g/10 minutes.

Another aspect of the invention is a process for making an ethylenepolymer extrusion composition comprising:

(a) combining 5 to 25 percent, by weight of the extrusion composition,of the at least one high pressure ethylene polymer composition with 75to 95 percent, by weight of the extrusion composition, of the at leastone ethylene α-olefin interpolymer composition, wherein the at least onehigh pressure ethylene polymer composition is combined using additionequipment that is part of the polymerization process used to prepare theat least one ethylene α-olefin interpolymer, to prepare an ethylenepolymer extrusion composition having a melt index, I₂, of at least 1.0g/10 minutes and a neck-in at a 1 mil monolayer extrusion coating weightof at least 12 percent lower than the expected neck-in value for thecomposition, and

(b) collecting or conveying the extrusion composition in a form suitablefor subsequent use.

Still another aspect of the invention is a process for using an ethylenepolymer extrusion composition to make an extrusion coated substrate, anextrusion profile or an extrusion cast film comprising:

(i) feeding an ethylene polymer composition into at least one extruderof an extrusion line, wherein the ethylene polymer composition comprisesfrom about 75 to 95 percent, by weight of the total composition, of atleast one ethylene/α-olefin interpolymer composition selected from thegroup consisting of a substantially linear ethylene polymer composition,a homogeneously branched linear ethylene polymer composition and aheterogeneously branched linear ethylene polymer composition, whereinthe ethylene/α-olefin polymer composition is characterized as having adensity in the range of 0.85 g/cc to 0.940 g/cc and a melt index, I₂, inthe range of 0.1 to 50 g/10 minutes, and from about 5 to 25 percent, byweight of the total composition, of at least high pressure ethylenepolymer composition characterized as having a melt index, I₂, less than1.0 g/10 minutes, a density of at least 0.916 g/cc, a melt strength ofat least 9 cN as determined using a Gottfert Rheotens unit at 190° C., aM_(w) /M_(n) ratio of at least 7.0 and a bimodal molecular weightdistribution as determined by gel permeation chromatography, and whereinthe ethylene polymer extrusion composition has a melt index, I₂, of atleast 1.0 g/10 minutes,

(ii) melting and mixing the ethylene polymer composition to form atleast one uniform molten polymer stream,

(iii) operating the extrusion line at line speeds greater than 152meters/minute,

(iii) extruding the molten polymer stream through a die to form aprimary extrudate, and either

(a) drawing down and cooling the extrudate to prepare the extrudedprofile of at least one layer of the ethylene polymer extrusioncomposition, or

(b) drawing down the extrudate onto the substrate to thereby coat thesubstrate with at least one layer of the ethylene polymer extrusioncomposition, or

(c) drawing down and cooling the extrudate onto a take-off device tomake the film with at least one layer of the ethylene polymer extrusioncomposition, and

(vi) conveying or collecting the profile, the coated substrate or thefilm for subsequent use.

A further aspect of the invention is an article comprising at least onelayer of an ethylene polymer extrusion composition, wherein theextrusion composition comprises from about 75 to 95 percent, by weightof the total composition, of at least one ethylenle/α-olefininterpolymer composition selected from the group consisting of asubstantially linear ethylene polymer composition, a homogeneouslybranched linear ethylene polymer composition and a heterogeneouslybranched linear ethylene polymer composition, wherein theethylene/α-olefin polymer is characterized as having a density in therange of 0.85 g/cc to 0.940 g/cc and from about 5 to 25 percent, byweight of the total composition, of at least one high pressure ethylenepolymer characterized as having a melt index, I₂, less than 6.0 g/10minutes, a density of at least 0.916 g/cc, a melt strength of at least 9cN as determined using a Gottfert Rheotens unit at 190° C., a M_(w)/M_(n) ratio of at least 7.0 and a bimodal molecular weight distributionas determined by gel permeation chromatography, and wherein the ethylenepolymer extrusion composition has a melt index, I₂, of at least 1.0 g/10minutes.

With the present invention, one obtains reduced neck-in, higher drawdownrates, and greater resistance to draw resonance than obtainable withknown polymer blends or unmodified ethylene α-olefin interpolymercompositions.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graphical illustration of the molecular weight distributionas determined using gel permeation chromatography of a high pressureethylene polymer composition suitable for use in the present invention.

FIG. 2 is a graphical illustration of the molecular weight distributionand the comparative bimodality (as determined using gel permeationchromatography) of four different high pressure ethylene polymercompositions.

FIG. 3 is a plot of melt strength versus neck-in at 1 mil for lowdensity polyethylene resins which is used to predict, by extrapolation,the neck-in performance of resins that can not be drawn down due toexcessive melt strength.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The inventive composition comprises from 75 to 95 percent, preferablyfrom 80 to 95 percent, more preferably from 85 to 95 percent, mostpreferably from 88 to 95 percent based on the total weight of thecomposition, of at least one ethylene α-olefin interpolymer compositionand from 5 to 25 percent, preferably from 5 to 20 percent, morepreferably from 5 to 15 percent, most preferably from 5 to 12 percentbased on the total weight of the composition, of at least one highpressure ethylene polymer composition.

Preferably, the actual or measured neck-in value of the inventiveethylene polymer extrusion composition will be at least 12 percent,preferably at least 16 percent, more preferably at least 24 percent,most preferably at least 30 percent lower than the expected neck-invalue for the composition based weight fractional contributions of thecomponent polymer compositions. The density of the inventive compositionwill in the range of 0.850 to 0.940 g/cc, preferably in the range of0.860 to 0.930 g/cc, more preferably in the range of 0.870 to 0.920g/cc, most preferably in the range of 0.880 to 0.915 g/cc. The meltindex, I₂, of the inventive composition with be in the range of 1 to 50g/10 minutes, preferably in the range of 1 to 30 g/10 minutes, morepreferably in the range of 1 to 20 g/10 minutes, most preferably in therange of 1.0 to 10 g/10 minutes. The melt strength of the inventivecomposition as determined using a Gottfert Rheotens will be at least 9centiNewton (cN), preferably at least 15 cN, more preferably at least 20cN, most preferably at least 25 cN.

Definition of Terms

The term "polymer", as used herein, refers to a polymeric compoundprepared by polymerizing monomers, whether of the same or a differenttype. The generic term polymer thus embraces the term "homopolymer",usually employed to refer to polymers prepared from only one type ofmonomer.

The term "interpolymer", as used herein, refers to polymers prepared bythe polymerization of at least two different types of monomers. Thegeneric term "interpolymer" thus includes the term "copolymers", whichis accurately employed to refer to polymers prepared from two differentmonomers. However, the term "copolymer" is also used in the art to referto polymers prepared from two or more different monomers.

The term "expected neck-in value", as used herein, in contrast to anactual, measured neck-in value, refers to the neck-in value expected orpredicted based on the weight fraction calculations and the individualneck-in values contributed by the component polymers of an extrusioncomposition. As an example of the calculation, where an extrusioncomposition comprises 90 weight percent of an ethylene α-olefininterpolymer which has an extrusion coating neck-in value at 1 mil of7.5 and 10 weight percent of a high pressure ethylene polymer which hasan extrusion coating neck-in value at 1 mil of 1.75 inches, theextrusion composition has an expected neck-in value of 6.9 inches where6.75 inches would be contributed by the ethylene α-olefin polymer and0.175 inch would be contributed by the high pressure ethylene polymer.

The term "high pressure ethylene polymer" or "highly branched ethylenepolyethylene" is defined herein to mean that the polymer is partly orentirely homopolymerized or interpolymerized in autoclave or tubularreactors at pressures above 14,500 psi (100 MPa) with the use offree-radical initiators.

The terms "homogeneous ethylene polymer" and "homogeneously branchedethylene polymer" are used in the conventional sense in reference to anethylene polymer in which the comonomer is randomly distributed within agiven polymer molecule and wherein substantially all of the polymermolecules have the same ethylene to comonomer molar ratio. Homogeneouslybranched ethylene polymers are characterized by a short chain branchingdistribution index (SCBDI) greater than or equal to 30 percent,preferably greater than or equal to 50 percent, more preferably greaterthan or equal to 90 percent and essentially lack a measurable highdensity (crystalline) polymer fraction. The SCBDI is defined as theweight percent of the polymer molecules having a comonomer contentwithin 50 percent of the median total molar comonomer content. Forpolyolefins, the SCBDI and presence of a high density polymer fractioncan be determined by well-known temperature rising elution fractionation(TREF) techniques, such as those described by Wild et al., Journal ofPolymer Science, Poly. Phys. Ed., Vol. 20, p. 441 (1982), L. D. Cady,"The Role of Comonomer Type and Distribution in LLDPE ProductPerformance," SPE Regional Technical Conference, Quaker Square Hilton,Akron, Ohio, October 1-2, pp. 107-119 (1985), or U.S. Pat. No.4,798,081, the disclosures of all which are incorporated herein byreference.

The term "substantially linear ethylene polymer" includes the term"substantially linear α-olefin polymer". Substantially linear αolefinpolymers contain long chain branches as well as short chain branchesattributable to homogeneous comonomer incorporation. The long chainbranches are of the same structure as the backbone of the polymer andare longer than the short chain branches. The polymer backbone ofsubstantially linear α-olefin polymers is substituted with an average of0.01 to 3 long chain branch/1000 carbons. Preferred substantially linearpolymers for use in the invention are substituted with from 0.01 longchain branch/1000 carbons to 1 long chain branch/1000 carbons, and morepreferably from 0.05 long chain branch/1000 carbons to 1 long chainbranches/1000 carbons.

Long chain branching is defined herein as a chain length of at least 6carbons, above which the length cannot be distinguished using ¹³ Cnuclear magnetic resonance spectroscopy. The long chain branch can be aslong as about the same length as the length of the polymer backbone towhich it is attached.

The presence of long chain branching can be determined in ethylenehomopolymers by using ³ C nuclear magnetic resonance (NMR) spectroscopyand is quantified using the method described by Randall (Rev. Macromol.Chem. Phys., C29, V. 2&3, p. 285-297), the disclosure of which isincorporated herein by reference.

As a practical matter, current ¹³ C nuclear magnetic resonancespectroscopy cannot determine the length of a long chain branch inexcess of six carbon atoms. However, there are other known techniquesuseful for determining the presence of long chain branches in ethylenepolymers, including ethylene/1-octene interpolymers. Two such methodsare gel permeation chromatography coupled with a low angle laser lightscattering detector (GPC-LALLS) and gel permeation chromatographycoupled with a differential viscometer detector (GPC-DV). The use ofthese techniques for long chain branch detection and the underlyingtheories have been well documented in the literature. See, e.g., Zimm,G.H. and Stockmayer, W. H., J. Chem. Phys., 17, 1301 (1949) and Rudin,A., Modern Methods of Polymer Characterization, John Wiley & Sons, NewYork (1991) pp. 103-112, both of which are incorporated by reference.

A. Willem deGroot and P. Steve Chum, both of The Dow Chemical Company,at the Oct. 4, 1994 conference of the Federation of Analytical Chemistryand Spectroscopy Society (FACSS) in St. Louis, Mo., presented datademonstrating that GPC-DV is a useful technique for quantifying thepresence of long chain branches in substantially linear ethyleneinterpolymers. In particular, deGroot and Chum found that the level oflong chain branches in substantially linear ethylene homopolymer samplesmeasured using the Zimm-Stockmayer equation correlated well with thelevel of long chain branches measured using ¹³ C NMR.

Further, deGroot and Chum found that the presence of octene does notchange the hydrodynamic volume of the polyethylene samples in solutionand, as such, one can account for the molecular weight increaseattributable to octene short chain branches by knowing the mole percentoctene in the sample. By deconvoluting the contribution to molecularweight increase attributable to 1-octene short chain branches, deGrootand Chum showed that GPC-DV may be used to quantify the level of longchain branches in substantially linear ethylene/octene copolymers.

deGroot and Chum also showed that a plot of Log(I₂, Melt Index) as afunction of Log(GPC Weight Average Molecular Weight) as determined byGPC-DV illustrates that the long chain branching aspects (but not theextent of long branching) of substantially linear ethylene polymers arecomparable to that of high pressures highly branched low densitypolyethylene (LDPE) and are clearly distinct from ethylene polymersproduced using Ziegler-type catalysts such as titanium complexes andordinary homogeneous catalysts such as hafnium and vanadium complexes.

For ethylene/α-olefin interpolymers, the long chain branch is longerthan the short chain branch that results from the incorporation of theα-olefin(s) into the polymer backbone. The empirical effect of thepresence of long chain branching in the substantial linearethylene/α-olefin interpolymers used in the invention is manifested asenhanced rheological properties which are quantified and expressedherein in terms of gas extrusion rheometry (GER) results and/or meltflow, I₁₀ /I₂, increases.

In contrast to the term "substantially linear ethylene polymer", theterm "linear ethylene polymer" means that the polymer lacks measurableor demonstrable long chain branches.

Description of the High Pressure Ethylene Polymer

The molecular architecture of the high pressure ethylene polymercomposition is critical with respect to the neck-in, melt strength andprocessability improvements of the final composition. The high pressureethylene polymer for use in the invention has a relative high meltstrength, i.e. at least 9 cN, preferably at least 15 cN, more preferablyat least 20 cN, most preferably at least 25 cN. The high pressureethylene polymer will be further characterized as having a bimodaldistribution as determined by gel permeation chromatography and a M_(w)/M_(n) will at least 7.0, preferably at least 7.3, more preferably atleast 7.6 The melt index, I₂, of the high pressure ethylene polymer foruse in preparing the extrusion composition of the invention is less than6.0 g/10 minutes, preferably less than 1.0 g/10 minutes, more preferablyless than 0.8 and most preferably less than 0.5 g/10 minutes. Thedensity of the high pressure ethylene polymer for use in the inventionis at least 0.916 g/cc, preferably at least 0.917, more preferably atleast 0.918 g/cc. The density of the high pressure ethylene polymercomposition will be higher when an interpolymer (e.g., copolymer orterpolymer) such as, for example ethylene-vinyl acetate-carbon monoxide(EVACO)) is used as the blend component polymer.

Preparation of the High Pressure Ethylene Polymer

The high pressure ethylene polymer composition selected for blendingwith the ethylene α-olefin interpolymer composition can be producedusing conventional high pressure polymerization techniques in anautoclave or tubular reactor using at least one free radical initiator.When an autoclave reactor is employed, the reaction zone can be a singlezone or multiple zone. Telogens such as, for example propylene andisobutane, can also be used as chain transfer agents. Preferably, thehigh pressure ethylene polymer is produced using an autoclave reactorwithout the addition of a telogen due to difficulty of manufacturingbimodal molecular weight distributions in a tubular process. However,the combination of an autoclave reactor in series or parallel with atubular reactor is also suitable for making the inventive compositionsince bimodal molecular weight distributions can be manufactured usingsuch techniques.

Suitable free-initiator for polymerizing ethylene at high reactorpressures are well known and include, but are not limited to, peroxidesand oxygen. Techniques for maximizing the melt strength of ethylenepolymers produced by high pressure polymerization are also known andinclude, but are not limited to, maximizing the reaction zonetemperature differential, multiple initiator injections, extendedreactor and post reactor residence times and higher gas inlettemperature.

Suitable High Pressure Ethylene Polymers

Suitable high pressure ethylene polymer compositions for use inpreparing the inventive extrusion composition include low densitypolyethylene (homopolymer) and ethylene interpolymerized with at leastone α,β-ethylenically unsaturated comonomers, e.g., acrylic acid,methacrylic acid, methyl acrylate and vinyl acetate. A suitabletechnique for preparing useful high pressure ethylene interpolymercompositions is described by McKinney et al. in U.S. Pat. No. 4,599,392,the disclosure of which is incorporated herein by reference.

While both high pressure ethylene homopolymers and interpolymers arebelieved to useful in the invention, homopolymer polyethylene ispreferred. When at least one high pressure ethylene interpolymercomposition is used, the preferred interpolymer composition willcomprise from 0.1 to 55 weight percent comonomer, more preferably from 1to 35 weight percent comonomer, and most preferably from 2 to 28 totalweight percent comonomer, based on the total weight of the interpolymercomposition.

Substantially Linear Ethylene α-olefin Polymers

The substantially linear ethylene α-olefin polymers used in the presentinvention are a unique class of compounds that are further defined inU.S. Pat. No. 5,278,236 and in U.S. Pat. No. 5,278,272, each of which isincorporated herein by reference.

Substantially linear ethylene polymers differ significantly from theclass of polymers conventionally known as homogeneously branched linearethylene/α-olefin copolymers described, for example, by Elston in U.S.Pat. No. 3,645,992. Substantially linear ethylene polymers also differsignificantly from the class of polymers known conventionally asheterogeneous Ziegler polymerized linear ethylene polymers (e.g., ultralow density polyethylene, linear low density polyethylene or highdensity polyethylene made, for example, using the technique disclosed byAnderson et al. in U.S. Pat. No. 4,076,698, incorporated herein byreference, and utilized by Dohrer et al. as described in U.S. Pat. No.4,780,264), and from the class known as free-radical initiated highlybranched high pressure low density ethylene homopolymer and ethyleneinterpolymers such as, for example, ethylene-acrylic acid (EAA)copolymers and ethylene-vinyl acetate (EVA) copolymers.

Preparation of Substantially Linear Ethylene Polymers

Single site polymerization catalyst, (e.g., the monocyclo-pentadienyltransition metal olefin polymerization catalysts described by Canich inU.S. Pat. No. 5,026,798 or by Canich in U.S. Pat. No. 5,055,438, thedisclosures of which are both incorporated herein by reference) orconstrained geometry catalysts (e.g., as described by Stevens et al. inU.S. Pat. No. 5,064,802, the disclosure of which incorporated herein byreference) can be used to prepare substantially linear ethylenepolymers, so long as the catalysts are used consistent with the methodsdescribed in U.S. Pat. No. 5,278,236 and in U.S. Pat. No. 5,278,272.Such polymerization methods are also described in PCT/U.S. 92/08812(filed Oct. 15, 1992), the disclosure of which is incorporated herein byreference. However, the substantially linear ethylene interpolymers andhomopolymers are preferably made by using suitable constrained geometrycatalysts, especially constrained geometry catalysts as disclosed inU.S. application Ser. Nos.: 545,403, filed Jul. 3, 1990; 758,654, filedSep. 12, 1991; 758,660, filed Sep. 12, 1991; and 720,041, filed Jun. 24,1991, the teachings of all of which are incorporated herein byreference.

Suitable cocatalysts for use herein include but are not limited to, forexample, polymeric or oligomeric aluminoxane especially methylaluminoxane or modified methyl aluminoxane (made, e.g., as described inU.S. Pat. No. 5,041,584, U.S. Pat. No. 4,544,762, U.S. Pat. No.5,015,749, and/or U.S. Pat. No. 5,041,585, the disclosures of each ofwhich are incorporated herein by reference) as well as inert,compatible, non-coordinating, ion forming compounds. Preferredcocatalysts are inert, non-coordinating, boron compounds.

The polymerization conditions for manufacturing the substantially linearethylene interpolymer compositions used in the present invention arepreferably those useful in the continuous solution polymerizationprocess, although the application of the present invention is notlimited thereto. Continuous slurry and gas phase polymerizationprocesses can also be used, provided the proper catalysts andpolymerization conditions are employed. To polymerize the substantiallylinear interpolymers and copolymers useful in the invention, the singlesite and constrained geometry catalysts mentioned earlier can be used,but for substantially linear ethylene polymers the polymerizationprocess should be operated such that the substantially linear ethylenepolymers are formed. That is, not all polymerization conditionsinherently make the substantially linear ethylene polymers, even whenthe same catalysts are used.

For example, in one embodiment of a polymerization process useful inmaking the novel substantially linear ethylene polymers, a continuousprocess is used, as opposed to a batch process.

Preferably, for substantially linear ethylene polymers, thepolymerization is performed in a continuous solution polymerizationprocess. Generally, manipulation of I₁₀ /I₂ while holding M_(w) /M_(n)relatively low for producing the substantially linear ethylene polymersusing constrained geometry catalyst technology described herein is afunction of reactor temperature and/or ethylene concentration. Reducedethylene concentration and higher temperature generally produces higherI₁₀ /I₂. Generally, as the ethylene concentration of the reactordecreases, the polymer concentration increases. For the novelsubstantially linear ethylene interpolymers and homopolymers, thepolymer concentration for a continuous solution polymerization processis preferably above about 5 weight percent of the reactor contents,especially above about 6 weight percent of the reactor contents.Generally, the polymerization temperature of the continuous process,using constrained geometry catalyst technology, is from about 20° C. toabout 250° C. If a narrow molecular weight distribution polymer (M_(w)/M_(n) of from about 1.5 to about 2.5) having a higher I₁₀ /I₂ ratio(e.g. I₁₀ /I₂ of about 7 or more, preferably at least about 8,especially at least about 9) is desired, the ethylene concentration inthe reactor is preferably not more than about 8 percent by weight of thereactor contents, especially not more than about 6 percent by weight ofthe reactor contents, and most especially not more than about 4 percentby weight of the reactor contents.

Description of Substantially Linear Ethylene Polymers

The substantially linear ethylene interpolymer compositions for use inthe invention are characterized as having

(a) a melt flow ratio, I₁₀ /I₂ ≧5.63,

(b) a molecular weight distribution, M_(w) /M_(n), as determined by gelpermeation chromatography and defined by the equation:

(M_(w) /M_(n))≦(I₁₀ /I₂)-4.63,

(c) a gas extrusion rheology such that the critical shear rate at onsetof surface melt fracture for the substantially linear ethylene polymeris at least 50 percent greater than the critical shear rate at the onsetof surface melt fracture for a linear ethylene polymer, wherein thesubstantially linear ethylene polymer and the linear ethylene polymercomprise the same comonomer or comonomers, the linear ethylene polymerhas an I₂, M_(w) /M_(n) and density within ten percent of thesubstantially linear ethylene polymer and wherein the respectivecritical shear rates of the substantially linear ethylene polymer andthe linear ethylene polymer are measured at the same melt temperatureusing a gas extrusion rheometer, and

(d) a single differential scanning calorimetry, DSC, melting peakbetween -30° and 150° C.

The substantially linear ethylene interpolymers used in this inventionessentially lack a measurable "high density" fraction as measured by theTREF technique. The substantially linear ethylene interpolymer generallydo not contain a polymer fraction with a degree of branching less thanor equal to 2 methyls/1000 carbons. The "high density polymer fraction"can also be described as a polymer fraction with a degree of branchingless than about 2 methyls/1000 carbons. Among other benefits, the lackof a high density polymer fraction permits improved coating smoothness,printability, optical properties as well as enhanced film/coatingflexibility and elasticity.

Determination of the critical shear rate and critical shear stress inregards to melt fracture as well as other rheology properties such as"rheological processing index" (PI), is performed using a gas extrusionrheometer (GER). The gas extrusion rheometer is described by M. Shida,R. N. Shroff and L. V. Cancio in Polymer Engineering Science, Vol. 17,No. 11, p. 770 (1977), and in "Rheometers for Molten Plastics" by JohnDealy, published by Van Nostrand Reinhold Co. (1982) on pp. 97-99, bothof which are incorporated by reference herein in their entirety. GERexperiments are performed at a temperature of 190° C., at nitrogenpressures between 250 to 5500 psig using a 0.0754 mm diameter, 20:1 L/Ddie with an entrance angle of 180°. For the substantially linearethylene polymers described herein, the PI is the apparent viscosity (inkpoise) of a material measured by GER at an apparent shear stress of2.15×10⁶ dyne/cm². The substantially linear ethylene polymer for use inthe invention are ethylene interpolymers having a PI in the range of0.01 kpoise to 50 kpoise, preferably 15 kpoise or less. Thesubstantially linear ethylene polymers used herein have a PI less thanor equal to 70 percent of the PI of a linear ethylene polymer (either aZiegler polymerized polymer or a linear uniformly branched polymer asdescribed by Elston in U.S. Pat. No. 3,645,992) having an I₂, M_(w)/M_(n) and density, each within ten percent of the substantially linearethylene polymers.

The rheological behavior of substantially linear ethylene polymers canalso be characterized by the Dow Rheology Index (DRI), which expresses apolymer's "normalized relaxation time as the result of long chainbranching." (See, S. Lai and G. W. Knight ANTEC '93 Proceedings, INSITE™Technology Polyolefins (ITP)--New Rules in the Structure/RheologyRelationship of Ethylene α-Olefin Copolymers, New Orleans, La., May1993, the disclosure of which is incorporated herein by reference). DRIvalues range from 0 for polymers which do not have any measurable longchain branching (e.g., Tafmer™ products available from MitsuiPetrochemical Industries and Exact™ products available from ExxonChemical Company) to about 15 and is independent of melt index. Ingeneral, for low to medium pressure ethylene polymers (particularly atlower densities) DRI provides improved correlations to melt elasticityand high shear flowability relative to correlations of the sameattempted with melt flow ratios. For the substantially linear ethylenepolymers useful in this invention, DRI is preferably at least 0.1, andespecially at least 0.5, and most especially at least 0.8. DRI can becalculated from the equation:

    DRI=(3652879*τ.sub.o.sup.1.00649 /η.sub.o -1)/10

where τ_(o) is the characteristic relaxation time of the material andη_(o) is the zero shear viscosity of the material. Both τ_(o) and η_(o)are the "best fit" values to the Cross equation, i.e.,

    η/η.sub.o =1/(1+(γ*τ.sub.o).sup.1-n)

where n is the power law index of the material, and η and γ are themeasured viscosity and shear rate, respectively. Baseline determinationof viscosity and shear rate data are obtained using a RheometricMechanical Spectrometer (RMS-800) under dynamic sweep mode from 0.1 to100 radians/second at 160° C. and a Gas Extrusion Rheometer (GER) atextrusion pressures from 1,000 psi to 5,000 psi (6.89 to 34.5 MPa),which corresponds to shear stress from 0.086 to 0.43 MPa, using a 0.0754mm diameter, 20:1 L/D die at 190° C. Specific material determinationscan be performed from 140° to 190° C. as required to accommodate meltindex variations.

An apparent shear stress versus apparent shear rate plot is used toidentify the melt fracture phenomena and quantify the critical shearrate and critical shear stress of ethylene polymers. According toRamamurthy in the Journal of Rheology, 30(2), 337-357, 1986, thedisclosure of which is incorporated herein by reference, above a certaincritical flow rate, the observed extrudate irregularities may be broadlyclassified into two main types: surface melt fracture and gross meltfracture.

Surface melt fracture occurs under apparently steady flow conditions andranges in detail from loss of specular film gloss to the more severeform of "sharkskin." Herein, as determined using the above-describedGER, the onset of surface melt fracture (OSMF) is characterized at thebeginning of losing extrudate gloss at which the surface roughness ofthe extrudate can only be detected by 40×magnification. The criticalshear rate at the onset of surface melt fracture for the substantiallylinear ethylene interpolymers and homopolymers is at least 50 percentgreater than the critical shear rate at the onset of surface meltfracture of a linear ethylene polymer having essentially the same I₂ andM_(w) /M_(n).

Gross melt fracture occurs at unsteady extrusion flow conditions andranges in detail from regular (alternating rough and smooth, helical,etc.) to random distortions. For commercial acceptability and maximumabuse properties of films, coatings and profiles, surface defects shouldbe minimal, if not absent. The critical shear stress at the onset ofgross melt fracture for the substantially linear ethylene polymercompositions used in the invention, especially those having adensity >0.910 g/cc, is greater than 4×10⁶ dynes/cm². The critical shearrate at the onset of surface melt fracture (OSMF) and the onset of grossmelt fracture (OGMF) will be used herein based on the changes of surfaceroughness and configurations of the extrudates extruded by a GER.Preferably, in the present invention, the substantially linear ethylenepolymer composition will be characterized by its critical shear rate,rather than its critical shear stress.

Melting Peak Determination

Substantially linear α-olefin polymers, like other homogeneouslybranched ethylene α-olefin polymer compositions consisting a singlepolymer component material, are characterized by a single DSC meltingpeak. The single melting peak is determined using a differentialscanning calorimeter standardized with indium and deionized water. Themethod involves 5-7 mg sample sizes, a "first heat" to about 140° C.which is held for 4 minutes, a cool down at 10°/min. to -30° C. which isheld for 3 minutes, and heat up at 10° C./mini. to 140° C. for the"second heat". The single melting peak is taken from the "second heat"heat flow vs. temperature curve. Total heat of fusion of the polymer iscalculated from the area under the curve.

For substantially linear ethylene polymer compositions having a densityof 0.875 g/cc to 0.910 g/cc, the single melting peak may show, dependingon equipment sensitivity, a "shoulder" or a "hump" on the low meltingside that constitutes less than 12 percent, typically, less than 9percent, and more typically less than 6 percent of the total heat offusion of the polymer. Such an artifact is observable for otherhomogeneously branched polymers such as Exact™ resins and is discernedon the basis of the slope of the single melting peak varyingmonotonically through the melting region of the artifact. Such anartifact occurs within 34° C., typically within 27° C., and moretypically within 20° C. of the melting point of the single melting peak.The heat of fusion attributable to an artifact can be separatelydetermined by specific integration of its associated area under the heatflow vs. temperature curve.

Molecular Weight Distribution Determination

The molecular weight distribution of the ethylene α-olefin interpolymercompositions and the high pressure ethylene polymer compositions aredetermined by gel permeation chromatography GPC on a Waters 150 hightemperature chromatographic unit equipped with differentialrefractometer and three columns of mixed porosity. The columns aresupplied by Polymer Laboratories and are commonly packed with pore sizesof 10³, 10⁴, 10⁵ and 10⁶ Å. The solvent is 1,2,4-trichlorobenzene, fromwhich 0.3 percent by weight solutions of the samples are prepared forinjection. The flow rate is 1.0 milliliters/minute, unit operatingtemperature is 140° C. and the injection size is 100 microliters.

The molecular weight determination with respect to the polymer backboneis deduced by using narrow molecular weight distribution polystyrenestandards (from Polymer Laboratories) in conjunction with their elutionvolumes. The equivalent polyethylene molecular weights are determined byusing appropriate Mark-Houwink coefficients for polyethylene andpolystyrene (as described by Williams and Ward in Journal of PolymerScience, Polymer Letters, Vol. 6, p. 621, 1968) to derive the followingequation:

    M.sub.polyethylene =a*(M.sub.polystyrene).sup.b.

In this equation, a=0.4316 and b=1.0. Weight average molecular weight,M_(w), is calculated in the usual manner according to the followingformula: M_(w) =Σw_(i) ×M_(i), where w_(i) and M_(i) are the weightfraction and molecular weight, respectively, of the i^(th) fractioneluting from the GPC column.

Comparative Description of Ethylene α-Olefin Polymer

Substantially linear ethylene polymers are known to have excellentprocessability, despite having a relatively narrow molecular weightdistribution (i.e., the M_(w) /M_(n) ratio is typically less than 3.5,preferably less than 2.5, and more preferably less than 2).Surprisingly, in light of disclosures by Dohrer and Niemann (U.S. Pat.No. 4,780,264 and ANTEC Proceedings 1989, "Resistance to Draw Resonanceof Linear Low Density Polyethylene Through Improved Resin Design", page28-30) and unlike homogeneously and heterogeneously branched linearethylene polymers, the melt flow ratio I₁₀ /I₂ of substantially linearethylene polymers can be varied essentially independently of themolecular weight distribution, M_(w) /M_(n). Accordingly, the preferredethylene α-olefin interpolymer for use in preparing the inventiveextrusion composition is a substantially linear ethylene polymer.

Substantially linear ethylene polymers are homogeneously branchedethylene polymers and are disclosed in U.S. Pat. No. 5,272,236 and U.S.Pat. No. 5,272,272, the disclosures of which are incorporated herein byreference. Homogeneously branched substantially linear ethylene polymersare available from The Dow Chemical Company as Affinity™ polyolefinplastomers, and as Engage™ polyolefin elastomers. Homogeneously branchedsubstantially linear ethylene polymers can be prepared by the continuoussolution, slurry, or gas phase polymerization of ethylene and one ormore optional α-olefin comonomers in the presence of a constrainedgeometry catalyst, such as is disclosed in European Patent application416,815-A, incorporated herein by reference. Preferably, a solutionpolymerization process is used to manufacture the substantially linearethylene interpolymer used in the present invention.

Homogeneously Branched Linear Ethylene Polymers

Although their molecular architecture differs significantly from that ofthe substantially linear ethylene polymer compositions, homogeneouslybranched linear ethylene polymer compositions are also useful in thisinvention.

Single site polymerization catalysts, (e.g., the monocyclo-pentadienyltransition metal olefin polymerization catalysts described by Canich inU.S. Pat. No. 5,026,798 or by Canich in U.S. Pat. No. 5,055,438, thedisclosures of which are both incorporated herein by reference) can beused to prepare homogeneously branched linear ethylene polymercompositions. As exemplified in U.S. Pat. No. 3,645,992 to Eiston,homogeneously branched linear ethylene polymer compositions can also beprepared in conventional polymerization processes using Ziegler-typecatalysts such as, for example, zirconium and vanadium catalyst systems.Another example is provided in U.S. Pat. No. 5,218,071 to Tsutsui et al.which discloses the use of catalyst systems based on hafnium for thepreparation of homogeneously branched linear ethylene polymer blends.

Homogeneously branched linear ethylene polymers are typicallycharacterized as having a molecular weight distribution, M_(w) /M_(n),of about 2. Commercial examples of homogeneously branched linearethylene polymer compositions suitable in the invention include thosesold by Mitsui Petrochemical Industries as Tafmer™ resins and by ExxonChemical Company as Exact™ resins.

Heterogeneously Branched Linear Ethylene Polymers

The terms "heterogeneous ethylene polymer" and "heterogeneously branchedethylene polymer" mean that the ethylene polymer is characterized as amixture of interpolymer molecules having various ethylene to comonomermolar ratios. Heterogeneously branched ethylene polymers arecharacterized as having a short chain branching distribution index(SCBDI) less than about 30 percent. All known heterogeneously branchedethylene polymers are linear and have no measurable or demonstrable longchain branching. Heterogeneously branched linear ethylene polymers areavailable from The Dow Chemical Company as Dowlex™ linear low densitypolyethylene and as Attane™ ultra-low density polyethylene resins.Heterogeneously branched linear ethylene polymers can be prepared by thecontinuous, batch or semi-batch solution, slurry or gas phasepolymerization of ethylene and one or more optional α-olefin comonomersin the presence of a Ziegler Natta catalyst, such as by the processdisclosed in U.S. Pat. No. 4,076,698 to Anderson et al., incorporatedherein by reference. Preferably, heterogeneously branched ethylenepolymers are typically characterized as having molecular weightdistributions, M_(w) /M_(n), in the range of from 3.5 to 4.1.

Suitable α-Olefin Comonomers

The homogeneously branched and heterogeneously branched ethyleneα-olefin interpolymer compositions useful in invention are interpolymersof ethylene and at least one α-olefin. Suitable α-olefins arerepresented by the following formula:

    CH.sub.2 ═CHR

where R is a hydrocarbyl radical having from one to twenty carbon atoms.The interpolymerization process can be a solution, slurry or gas phasetechnique or combinations thereof. Suitable α-olefins for use ascomonomers include 1-propylene, 1-butene, 1-isobutylene, 1-pentene,1-hexene, 4-methyl-1-pentene, 1-heptene and 1-octene, as well as othermonomer types such as styrene, halo- or alkyl-substituted styrenes,tetrafluoro-ethylene, vinyl benzocyclobutane, 1,4-hexadiene,1,7-octadiene, and cycloalkenes, e.g., cyclopentene, cyclohexene andcyclooctene. Preferably, the α-olefin will be 1-butene, 1 -pentene,4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, or mixture thereof.More preferably, the α-olefin will be 1-hexene, 1-heptene, 1-octene, ormixtures thereof, as coatings, profiles and films fabricated with theresultant extrusion composition will have especially improved abuseproperties where such higher α-olefins are utilized as comonomers.However, most preferably, the α-olefin will be 1-octene and thepolymerization process will be a continuous solution process.

Ethylene α-Olefin Polymer Density and Molecular Weight

The density of the ethylene α-olefin interpolymers, as measured inaccordance with ASTM D-792, for use in the present invention isgenerally in the range of 0.850 grams/cubic centimeter (g/cc) to 0.940g/cc, preferably from 0.86 g/cc to 0.930 g/cc, more preferably from0.870 g/cc to 0.920 g/cc, and most preferably, from 0.88 g/cc to 0.915g/cc.

The molecular weight of ethylene polymers is conveniently indicatedusing a melt index measurement according to ASTM D-1238, Condition190C/2.16 kilogram (kg), formerly known as "Condition E" and also knownas I₂. Melt index is inversely proportional to the molecular weight ofthe polymer. Thus, the higher the molecular weight, the lower the meltindex, although the relationship is not linear. The melt index for theethylene α-olefin interpolymers useful herein is generally from 1gram/10 minutes (g/10 min.) to 50 g/10 min., preferably from 1 g/10 min.to 30 g/10 min., more preferably from 1 g/10 min. to 20 g/10 min., morepreferably from 1.0 g/10 min. to 10 g/10 minutes.

Other measurements useful in characterizing the molecular weight ofethylene α-olefin interpolymers compositions involve melt indexdeterminations with higher weights, such as, for common example, ASTMD-1238, Condition 190C/10 kg (formerly known as "Condition N" and alsoknown as I₁₀). "Melt flow ratio" is defined herein as the ratio of ahigher weight melt index determination to a lower weight determination,and for measured I₁₀ and the I₂ melt index values, the melt flow ratiois conveniently designated as I₁₀ /I₂. The I₁₀ /I₂ ratio of the ethyleneα-olefin interpolymer component is preferably at least about 5.63, andespecially from about 5.63 to about 18, and most especially from about 6to about 15.

Preparation of the Ethylene Polymer Extrusion Composition

The ethylene polymer extrusion compositions of this invention can beprepared by any suitable means known in the art including tumbledry-blending, weigh feeding, solvent blending, melt blending viacompound or side-arm extrusion, or the like as well as combinationsthereof. Multiple reactor polymerization processes can also be used inmaking the at least one ethylene α-olefin interpolymers useful inpreparing the ethylene polymer composition of the present invention.Examples of suitable multiple reactor ethylene α-olefininterpolymerization techniques are those disclosed in copendingapplications Ser. No. 07/815,716 filed Dec. 30, 1991 and Ser. No.08/010,958 filed Jan. 29, 1993, and in U.S. Pat. No. 3,914,342, thedisclosures of all of which are incorporated herein by reference. Themultiple reactors can be operated in series or in parallel or acombination thereof, with at least one homogeneous single-site type orheterogeneous Ziegler-type catalyst employed in at least one of thereactors or in both reactors.

When a multiple reactor technique is used to make the ethylene α-olefininterpolymer component of the invention, the high pressure ethylenepolymer component can be added by side-arm extrusion or weigh feedequipment situated downstream of the multiple reactors but directlyconnected to the primary manufacturing stream, or by subsequentincorporation in a different manufacturing unit or even at converterfacilities.

The inventive extrusion composition can also be blended with otherpolymer materials and can be used to prepare monolayer or multilayerarticles and structures, for example, as a sealant, adhesive or tielayer. The other polymer materials can be blended with the inventivecomposition to modify processing, film strength, heat seal, or adhesioncharacteristics.

Both the high pressure ethylene polymer composition and the ethyleneα-olefin interpolymer composition can be used in a chemically and/orphysically modified form to prepare the inventive composition. Suchmodifications can be accomplished by any known technique such as, forexample, by ionomerization and extrusion grafting.

Additives such as antioxidants (e.g., hindered phenolics such asIrganox® 1010 or Irganox® 1076 supplied by Ciba Geigy), phosphites(e.g., Irgafos® 168 also supplied by Ciba Geigy), cling additives (e.g.,PIB), Standostab PEPQ™ (supplied by Sandoz), pigments, colorants,fillers, and the like can also be included in the ethylene polymerextrusion composition of the present invention, to the extent that theydo not interfere with the high drawdown and substantially reducedneck-in discovered by Applicants. The article made from or using theinventive composition may also contain additives to enhance antiblockingand coefficient of friction characteristics including, but not limitedto, untreated and treated silicon dioxide, talc, calcium carbonate, andclay, as well as primary, secondary and substituted fatty acid amides,chill roll release agents, silicone coatings, etc. Other additives mayalso be added to enhance the anti-fogging characteristics of, forexample, transparent cast films, as described, for example, by Niemannin U.S. Pat. No. 4,486,552, the disclosure of which is incorporatedherein by reference. Still other additives, such as quaternary ammoniumcompounds alone or in combination with ethylene-acrylic acid (EAA)copolymers or other functional polymers, may also be added to enhancethe antistatic characteristics of coatings, profiles and films of thisinvention and allow, for example, the packaging or making ofelectronically sensitive goods.

Multilayered constructions comprising the inventive composition can beprepared by any means known including coextrusion, laminations and thelike and combinations thereof. Moreover, compositions of this inventioncan be employed in coextrusion operations where a higher drawdownmaterial is used to essentially "carry" one or more lower drawdownmaterials.

The ethylene polymer extrusion compositions of this invention, whetherof monolayer or multilayered construction, can be used to make extrusioncoatings, extrusion profiles and extrusion cast films. When theinventive composition is used for coating purposes or in multilayeredconstructions, substrates or adjacent material layers can be polar ornonpolar including for example, but not limited to, paper products,metals, ceramics, glass and various polymers, particularly otherpolyolefins, and combinations thereof. For extrusion profiling, variousarticles can be fabricated including, but not limited to, refrigeratorgaskets, wire and cable jacketing, wire coating, medical tubing andwater piping. Extrusion cast film made from or with the inventivecomposition can be used in food packaging and industrial stretch wrapapplications.

EXAMPLES

The following examples illustrate some of the particular embodiments ofthe present invention, but the following should not be construed to meanthe invention is limited to the particular embodiments shown. Also,practitioners of these arts will appreciate that the maximum line speedsattainable with one type of extruder or coater will not necessarily bethe same as the speeds attainable with another and, as such, the sameequipment arrangement should be used to provide meaningful comparisonsand to appreciate the advantages discovered by the Applicants.

Melt strength determinations are made at 190° C. using a GoettfertRheotens and an Instron capillary rheometer. The capillary rheometer isaligned and situated above the Rheoten unit and delivers, at a constantplunger speed of 25.4 mm/min, a filament of molten polymer to theRheotens unit. The Instron is equipped with a standard capillary die of2.1 mm diameter and 42 mm length (20:1 L/D) and delivers the filament tothe toothed take-up wheels of the Rheotens unit rotating at 10 mm/s. Thedistance between the exit of the Instron capillary die and the nip pointon the Rheotens take-up wheels was 100 mm. The experiment to determinemelt strength begins by accelerating the take-up wheels on the Rheotensunit at 2.4 mm/s², the Rheotens unit is capable of acceleration ratesfrom 0.12 to 120 mm/s². As the velocity of the Rheoten take-up wheelsincrease with time, the draw down force was recorded in centiNewtons(cN) using the Linear Variable Displacement Transducer (LVDT) on theRheotens unit. The computerized data acquisition system of the Rheotensunit records the draw down force as a function of take-up wheelvelocity. The actual melt strength value is taken from the plateau ofthe recorded draw down force. The velocity at filament break is alsorecorded in mm/s as the melt strength break speed.

Inventive Examples 1-3 and Comparative Examples 4-15

Table 1 summarizes the polymer compositons used in an extrusion coatingand melt strength evaluation. Sample A and B are substantially linearethylene/1-octene interpolymers manufactured according to the teachingsprovided by Lai et al. in U.S. Pat. Nos. 5,278,236 and 5,278,272. SampleC is a homogeneously branched linear ethylene/1-hexene interpolymersupplied by Exxon Chemical Company under the commercial designation ofExact™ 3022. Samples D-I are all high pressure ethylene polymersmanufactured by The Dow Chemical Company. Sample E is manufactured usingconventional tubular reactor techniques. Samples D and F-I aremanufactured using conventional autoclave reactor techniques. As anexample of the polymerization requirements to prepare a suitable highpressure ethylene polymer for use in the present invention, Table 2summarizes the polymerization conditions used manufacturing Sample D.The reactor employed is a 15 inch, 10:1 L/D constant-stirred, continuousautoclave reactor. Samples D-I all contain 200-300 ppm Irganox™ 1010antioxidant and Sample C contains (according to infra-red analysisfollowing solvent extraction of pressed film of the sample) 230 ppm ofactive Irganox™ 1076 antioxidant, both antioxidants are supplied byCiba-Geigy Chemical Company.

                                      TABLE 1                                     __________________________________________________________________________                          Melt                                                            Melt          Strength                                                        Index, I.sub.2                                                                         Melt Break                                                                              GPC                                                    Polymer                                                                           (g/10                                                                              Density                                                                           Strength,                                                                          Speed                                                                              Mw/Mn                                                                             GPC                                            Sample                                                                            Type                                                                              min.)                                                                              (g/cc)                                                                            (cN) (mm/s)                                                                             Ratio                                                                             Bimodality                                     __________________________________________________________________________    A   SLEP                                                                              4.75 0.910                                                                             1.30 269  2.11                                                                              No                                             B   SLEP                                                                              6.0  0.900                                                                             1.27 160  2.18                                                                              No                                             C   HLEP                                                                              10   0.905                                                                             0.349                                                                              303  2.32                                                                              No                                             D   LDPE                                                                              0.42 0.918                                                                             25.4 103  7.6 Yes                                            E   LDPE                                                                              0.26 0.921                                                                             17.7 124  <6  No                                             F   LDPE                                                                              10.9 0.919                                                                             4.70 273  6.02                                                                              No                                             G   LDPE                                                                              5.49 0.916                                                                             9.7  233  7.42                                                                              Yes                                            H   LDPE                                                                              3.17 0.924                                                                             8.88 186  5.78                                                                              Yes                                            I   LDPE                                                                              7.74 0.917                                                                             7.56 247  6.97                                                                              No                                             __________________________________________________________________________     SLEP = substantially linear ethylene polymer prepared by the                  interpolymerization of ethylene and 1octene.prepared in a continuous          solution polymerization process using a constrained geometry catalyst         system.                                                                       HLEP = a homogeneous linear ethylene polymer, Exact ™ 3022 supplied by     Exxon Chemical Company                                                        LDPE = high pressure low density polyethylene                            

                  TABLE 2                                                         ______________________________________                                        Autoclave Reactor Conditions                                                  ______________________________________                                        Reactor Pressure, psi    21,300                                               Zone 1 Temperature, °C.                                                                         235                                                  Zone 2 Temperature, °C.                                                                         235                                                  Zone 3 Temperature, °C.                                                                         254                                                  Zone 4 Temperature, °C.                                                                         282                                                  Top (Zone 1) Gas Inlet Temperature, °C.                                                         70                                                   Bottom (Zones 2) Gas Inlet Temperature, °C.                                                     28                                                   Recycle Rate, lbs/hr     1,500                                                High Pressure Separator Pressure, psi                                                                  1,650                                                Low Pressure Separator Pressure, psi                                                                   4                                                    Zone 1 Initiator Type    50/50 TPO/TPA                                                                 Mix                                                  Zone 1 Initiator Concentration, wt % in Isopar ™ C                                                  20                                                   Zone 1 Initiator Feed Rate, lbs/hr                                                                     17.5                                                 Zone 2 Initiator Type    50/50 TPO/TPA                                                                 Mix                                                  Zone 2 Initiator Concentration, wt % in Isopar ™ C                                                  20                                                   Zone 2 Initiator Feed Rate                                                                             14.8                                                 Zone 3 Initiator Type    100% TPA                                             Zone 3 Initiator Concentration, wt % in Isopar ™ C                                                  20                                                   Zone 3 Initiator Feed Rate                                                                             6.8                                                  Zone 4 Initiator Type    50/50 TPA/DTBP                                                                Mix                                                  Zone 4 Initiator Concentration, wt % in Isopar ™ C                                                  20                                                   Zone 4 Initiator Feed Rate                                                                             16.8                                                 High Pressure Level      Gassed Out                                           Low Pressure Separator Level, % by volume                                                              40                                                   Production Rate, lbs./hr 7,406                                                Secondary Processing     None                                                 ______________________________________                                         TPO = tertbutyl peroctoate; TPA = tertbutyl peracetate; DTBP =                ditert-butyl peroxide Isopar ™ C is an isoparafinic hydrocarbon solven     with a boiling range of 95-108° C. supplied by Exxon Chemical          Company                                                                  

FIG. 1 illustrates the molecular weight distribution (MWD) of Sample Das determined by gel permeation chromatography (GPC) is bimodal (i.e.,the polymer composition is characterized as having a distinct highmolecular hump). FIG. 2 shows that Samples G and I have bimodalmolecular weight distribution, whereas Samples F and H do not exhibitdistinct bimodality. Table 1 indicates that Samples D and G haverelatively high melt strength, broad molecular weight distributions, andbimodality, and as such these materials are considered suitable blendcomponent compositions for imparting improved extrusion properties.

Table 3 summarizes the blend compositions that are prepared from theindividual polymer compositions listed in Table 1. The blendcompositions were prepared either by melt mixing in a Haake torque mixeror by weigh feeding the components directly into the primary extruder ofthe extrusion coating line in accordance with the weight percentagesshown in Table 3.

                  TABLE 3                                                         ______________________________________                                        Sample                                                                              Exam-   Exam-   Exam- *Comp. *Comp.                                     Weight                                                                              ple     ple     ple   Example                                                                              Example                                                                              Example                             Percent                                                                             1       2       3     4      5      6                                   ______________________________________                                        B     95      90      80    100    90     90                                  D      5      10      20                                                      E                                  10                                         G                                         10                                  ______________________________________                                        Sample                                                                              *Comp.   Exam-   *Comp.                                                                              *Comp.                                                                              *Comp. *Comp.                              Weight                                                                              Example  ple     Exam- Exam- Example                                                                              Example                             Percent                                                                             7        8       ple 9 ple 10                                                                              11     12                                  ______________________________________                                        B     90       80                                                             C                                         100                                 D                      100                                                    E                            100                                              F                                  100                                        G              20                                                             I     10                                                                      ______________________________________                                        Sample           *Comp.      *Comp. *Comp.                                    Weight  Example  Example     Example                                                                              Example                                   Percent 13       14          15     16                                        ______________________________________                                        A                                   100                                       C       90                                                                    D       10                                                                    H                100                                                          I                            100                                              ______________________________________                                         *Not an example of the present invention; provided for comparative            purposes only.                                                           

Examples 1-3, 6, 8 and 13 and Comparative Examples 4, 5, 7, 11-12, and14-16 are evaluated for high drawn down performance on an extrusioncoating line. The coating equipment consists of a three-extruder BlackClawson coextrusion coating line with a 3 1/2 inch (8.9 cm) diameterprimary extruder with a 30:1 L/D, a 2 1/2 inch (6.4 cm) diametersecondary extruder with a 24:1 L/D and a 2 inch diameter secondaryextruder. A 76 cm slot coextrusion feedblock die is attached to theprimary extruder and deckled to 69 cm with a 20 mil die gap and a 6 inch(15.2 cm) air/draw gap. The line is controlled by a microprocessorsystem that include weight cell feed hoppers for rate checks and coatingweight control. The extrusion line is also equipped with a matte finish,glycol cooled chill roll set at 57° F. The targeted extrusiontemperature and screw speed for all extrusion coating examples is 625°F. and 90 rpm, respectively, unless otherwise noted. However, Example 13and Comparative Examples 14 and 18 were extrusion coated at a extrusionmelt temperature of about 612° F. Molten extrudate or webs for allexamples are drawn down continuously onto 50 lb. Kraft paper.

The evaluation involves systematically increasing the line/take-offspeed while maintaining a constant screw speed (90 rpm) until drawresonance is observed or web breakage occurs. The line speed at whichthe onset of draw resonance (i.e., web began to oscillate) is initiallyobserved or at which web breakage occurs, is taken as the ultimate ormaximum drawdown rate. The drawdown rate, neck-in measured at a 440 fpm(134 mpm) line speed for a 1 mil coating thickness, extruder amperage,die pressure, expected neck-in performance and the percent neck-in lowerthan expected for the examples are summarized in Table 4.The componentneck-in contribution for Samples D and E are taken by extrapolation fromFIG. 3 since these materials could not be extrusion coated as singlecomponent polymer compositions. The expected neck-in performance istaken from a linear blend rule equation as exemplified above.

                  TABLE 4                                                         ______________________________________                                        Extrusion Coating Results on                                                  Draw Resonance and Neck-In                                                                                 Neck-In                                                                       at 134       Percent                             Ex-  Die     Ex-     Drawdown                                                                              mpm/7 Expected                                                                             Lower                               am-  Pressure                                                                              truder  Rate†                                                                          Mil   Neck-In                                                                              than                                ple  (psi)   Amps    ft/min. (in)  (in)   Expected                            ______________________________________                                         1   1,560   147     >1,800  6.25  7.14   12.5                                 2   1,610   149     >1,700  4.375 6.78   35.5                                 3   1,690   148     1,260   3.25  6.06   46.3                                 4*  1,740   145     590     7.5   NA     NA                                   5*  1,610   149     1,300   6.125 6.83   10.3                                 6   1,500   145     >1,600  5.75  6.89   16.5                                 7*  1,700   137     1,600   6.125 6.93   11.6                                 8   1,490   138     >1,600  4.375 6.28   30.3                                 9*  ND      ND      ND      ND    0.25** NA                                   10* ND      ND      ND      ND    0.45** NA                                   11* ND      ND      1,460   1.8   NA     NA                                   12* 1,090   164     670     9.25  NA     NA                                  13   1,160   167     >1,600  4.125 8.35   50.6                                 14* ND      ND      980     2.0   NA     NA                                   15* 1,150    97     1,150   1.75  NA     NA                                   16* 1,000   135     670     6.75  NA     NA                                  ______________________________________                                         †Drawdown rate = takeoff spend at which dimensional irregularities     are observed to initially occur or the takeoff instantaneous to web           breakage.                                                                     *Not an example of the present invention; provided for comparative            purposes.                                                                     **Neckin value extrapolated from FIG. 3 based on melt strength                determination.                                                                ND = not determined.                                                          NA = not applicable.                                                     

As can be observed from the data in Table 4, extrusion coatingcompositions comprising high pressure ethylene polymers characterized ashaving high melt strength and a broad, bimodal molecular distributionallow substantially reduced neck-in performance relative to unmodifiedethylene α-olefin interpolymer compositions. However, surprisingly, theneck-in performance of such Compositions is also significantly lowerthan expected based on respective component materials.

In another evaluation, the heat seal, hot tack, adhesion and tearproperties of Example 1 is determined and compared to severalcommercially available sealant extrusion coating resins. Two differentmultilayered structures are used for the heal seal and hot tackdetermination. The structures are as follows:

Structure A:

48 gauge Hostaphan™ 2DEF/0.5 mil Primacor™ 4608/Example

Structure B:

30 lbs. Bleached Machine-Grade Kraft Paper/0.75 mil Primacor 3460/0.0035gauge A-Type Wettable Aluminum Foil/Example

Hostaphan 2DEF is a polyester film supplied by Hoechst Diafoil andPrimacor resins 4608 and 3460 are ethylene acrylic acid (EAA)interpolymers supplied by The Dow Chemical Comnpany.

For adhesion determinations, 0.035 gauge A-Type wettable Aluminum foiland 50 gauge oriented polypropylene are separately slip-sheeted at thecoater die while the Example is being coated at 400 fpm. Adhesion istaken as resistance to delamination or separation and is ratedqualitatively from excellent to poor where an "excellent" rate denotethe Example is highly resistance to separation when pulled manually.

Tear properties are determined in accordance with ASTM D1922 and isreported in grams. Tear strength is measured both in the machinedirection (MD) and in the cross direction (CD) for the Example coated at440 fpm onto 50-lb. Kraft paper. The term "tear strength" is used hereinto represent the average between MD and CD Elmendorf tear values and,likewise, is reported in grams.

Heat seal initiation temperature is defined as the minimum temperaturefor a 2 lb/in (0.4 kg/cm) seal strength. Heat seal testing is done on aTopwave Hot Tack Tester using a 0.5 second dwell time with a 40 psi(0.28 MPa) seal bar pressure. The seals are made at 5° increments in therange of 60-160° C. by folding the sealant layer over and sealing it toitself. The so-formed seals are pulled 24 hours after they are madeusing an Instron tensiometer at a 10 in/mm. (51 cm/min.) crosshead rate.The heat seal strength is taken as the highest strength in pounds perinch for the Example in the temperature range of 60°-160° before thesealing bar burns-through the sealant layer.

Hot tack initiation temperature is defined as the minimum sealtemperature required to develop a 4 Newton/in (1.6 N/cm) seal strength.Hot tack testing is performed using a Topwave Hot Tack Tester set at a0.5 second dwell, 0.2 second delay time, and 40 psi (0.28 MPa) seal barpressure. Hot tack seals are made at 5° increments in the temperaturerange of 60°-160° C. by folding the sealant layer over and hot tacksealing it to itself. The peel rate applied to the so-formed hot tackseals is of 150 mm/sec. The tester pulls the seal immediately after the0.2 second delay. Hot tack strength is taken as the maximum N/in valuein the 60°-160° C. temperature range for the Example. The hot tackwindow is taken as the temperature range where the hot tack strengthis >4 Newtons for Structure A and >8 Newtons for Structure B. Table 5illustrates the comparative performance properties of Example 1.

                  TABLE 5                                                         ______________________________________                                                    Example                                                                       1     15      17      18    19                                    ______________________________________                                        Extrusion Temperature, °F.                                                           610     618     614   550   550                                 Heat Seal Initiation, °C.                                              Structure A   82      95      105   83    85                                  Structure B   97      105     117   ND    ND                                  Heat Seal Strength, lbs/in                                                    Structure A   14.0    10.0    10.0  9.5   10.0                                Structure B   7.8     7.0     7.0         7.5                                 Hot Tack Initiation, °C.                                               Structure A   95      CND     CND   87    90                                  Structure B   98      112     117   94    95                                  Hot Tack Strength, N/in                                                       Structure A   8.5     2.5     3     10    10                                  Structure B   16      9       8           14.5                                Hot Tack Window, °C.                                                   Structure B > 8 Newtons                                                                     70      15      5     75    75                                  Structure A > 4 Newtons                                                                     25      0       0     65    65                                  Adhesion Rating                                                               Aluminum Foil G       F       G     E     E                                   Oriented Polypropylene                                                                      E       P       P     P     P                                   Elmendorf Tear Strength, g                                                                  327     121     240   ND    ND                                  ______________________________________                                         E = excellent; G = good; F = fair; P = poor; ND = not determined; CND =       could not determine since hot tack strength did not exceed 4 Newtons at       any temperature. *Not an example of the invention; provided for               comparative purposes. Comparative Examples 17 and 18 is Dowlex 3010 and       Primacor 3440, both of which are supplied by The Dow Chemical Company.        Comparative Example 19 is Surlyn ionomer 1652 which is supplied by Dupont     Chemical Company.                                                        

Table 5 shows Inventive Example 1 has excellent sealant properties,making it useful as a sealant layer in both monolayer or multilayerconstructions.

We claim:
 1. An ethylene polymer extrusion composition comprising fromabout 75 to 95 percent, by weight of the total composition, of at leastone substantially linear ethylene/α-olefin polymer, wherein thesubstantially linear ethylene/α-olefin polymer is characterized ashaving a density in the range of 0.85 g/cc to 0.940 g/cc and is furthercharacterized as having:(a) a melt flow ratio, I₁₀ /I₂ ≧5.63, (b) amolecular weight distribution, M_(w) /M_(n), as determined by gelpermeation chromatography and defined by the equation:

    (M.sub.w /M.sub.n)≦(I.sub.10 /I.sub.2)-4.63,

(c) a gas extrusion rheology such that the critical shear rate at onsetof surface melt fracture for the substantially linear ethylene polymeris at least 50 percent greater than the critical shear rate at the onsetof surface melt fracture for a linear ethylene polymer, wherein thesubstantially linear ethylene/α-olefin polymer and the linear ethylenepolymer comprise the same comonomer or comonomers, the linear ethylenepolymer has an I₂, M_(w) /M_(n) and density within ten percent of thesubstantially linear ethylene polymer and wherein the respectivecritical shear rates of the substantially linear ethylene/α-olefinpolymer and the linear ethylene polymer are measured at the same melttemperature using a gas extrusion rheometer, and (d) a singledifferential scanning calorimetry, DSC, melting peak between-30 and 150°C., andfrom about 5 to 25 percent, by weight of the total composition,of at least one high pressure ethylene polymer characterized as having amelt index, I₂, less than 6.0 g/10 minutes, a density of at least 0.916g/cc, a melt strength of at least 9 cN as determined using a GottfertRheotens unit at 190° C., a M_(w) /M_(n) ratio of at least 7.0 and abimodal molecular weight distribution as determined by gel permeationchromatography, wherein the ethylene polymer extrusion composition has amelt index, I₂, of at least 1.0 g/10 minutes.
 2. The composition ofclaim 1, wherein the substantially linear ethylene polymer has about0.01 to about 3 long chain branches/1000 carbons.
 3. The composition ofclaim 2, wherein the substantially linear ethylene polymer has at leastabout 0.1 long chain branch/1000 carbons.
 4. The composition of claim 3,wherein the substantially linear ethylene polymer has at least about 0.3long chain branch/1000 carbons.
 5. The composition of claim 1, whereinthe α-olefin is at least one C₃ -C₂₀ α-olefin.
 6. The composition ofclaim 5, wherein the α-olefin is selected from the group consisting of1-propylene, 1-butene, 1-isobutylene, 1-hexene, 4-methyl-1-pentene,1-pentene, 1-heptene and 1-octene.
 7. The composition of claim, 1wherein the ethylene α-olefin interpolymer is a copolymer of ethyleneand 1-octene and the high pressure ethylene polymer is an ethylenehomopolymer.
 8. The composition of claim 1, wherein the at least onehigh pressure ethylene polymer composition is an ethylene homopolymer.9. The composition of claim 1, wherein the at least one high pressureethylene polymer composition is an interpolymer of ethylene and at leastone unsaturated comonomer.
 10. A process for making an ethylene polymerextrusion composition comprising:(a) combining 5 to 25 percent, byweight of the extrusion composition, of the at least one high pressureethylene polymer composition with 75 to 95 percent, by weight of theextrusion composition, of at least one substantially linearethylene/α-olefin polymer which is characterized as havingi. a melt flowratio, I₁₀ /I₂ ≧5.63, ii. a molecular weight distribution, M_(w) /M_(n),as determined by gel permeation chromatography and defined by theequation:

    (M.sub.w /M.sub.n)≦(I.sub.10 /I.sub.2)-4.63

iii. a gas extrusion rheology such that the critical shear rate at onsetof surface melt fracture for the substantially linear ethylene polymeris at least 50 percent greater than the critical shear rate at the onsetof surface melt fracture for a linear ethylene polymer, wherein thesubstantially linear ethylene/α-olefin polymer and the linear ethylenepolymer comprise the same comonomer or comonomers, the linear ethylenepolymer has an I₂, M_(w) /M_(n) and density within ten percent of thesubstantially linear ethylene polymer and wherein the respectivecritical shear rates of the substantially linear ethylene/α-olefinpolymer and the linear ethylene polymer are measured at the same melttemperature using a gas extrusion rheometer, and iv. a singledifferential scanning calorimetry, DSC, melting peak between-30 and 150°C., wherein the at least one high pressure ethylene polymer compositionis combined using addition equipment that is part of the polymerizationprocess used to prepare the at least one substantially linearethylene/α-olefin polymer, to prepare an ethylene polymer extrusioncomposition having a melt index, I₂, of at least 1.0 g/10 minutes and aneck-in at a 1 mil monolayer extrusion coating weight of at least 12percent lower than the expected neck-in value for the composition, and(b) collecting or conveying the extrusion composition in a form suitablefor subsequent use.
 11. A process for using an ethylene polymerextrusion composition to make an extrusion coated substrate, anextrusion profile or an extrusion cast film comprising:(i) feeding anethylene polymer composition into at least one extruder of an extrusionline, wherein the ethylene polymer composition comprises from about 75to 95 percent, by weight of the total composition, of at least onesubstantially linear ethylene/α-olefin polymer, wherein thesubstantially linear ethylene/α-olefin polymer composition ischaracterized as having a density in the range of 0.85 g/cc to 0.940g/cc and a melt index, I₂, in the range of 0.1 to 50 g/10 minutes, andis further characterized as having:(a) a melt flow ratio, I₁₀ /I₂ ≧5.63(b) a molecular weight distribution, M_(w) /M_(n), as determined by gelpermeation chromatography and defined by the equation:

    (M.sub.w /M.sub.n)≦(I.sub.10 /I.sub.2)-4.63

(c) a gas extrusion rheology such that the critical shear rate at onsetof surface melt fracture for the substantially linear ethylene polymeris at least 50 percent greater than the critical shear rate at the onsetof surface melt fracture for a linear ethylene polymer, wherein thesubstantially linear ethylene/α-olefin polymer and the linear ethylenepolymer comprise the same comonomer or comonomers, the linear ethylenepolymer has an I₂, M_(w) /M_(n) and density within ten percent of thesubstantially linear ethylene polymer and wherein the respectivecritical shear rates of the substantially linear ethylene/α-olefinpolymer and the linear ethylene polymer are measured at the same melttemperature using a gas extrusion rheometer, and (d) a singledifferential scanning calorimetry DSC, melting peak between<30 and 150°C. and from about 5 to 25 percent, by weight of the total composition,of at least high pressure ethylene polymer composition characterized ashaving a melt index, I₂, less than 1.0 g/10 minutes, a density of atleast 0.916 g/cc, a melt strength of at least 9 cN as determined using aGottfert Rheotens unit at 190° C., a M_(w) /M_(n) ratio of at least 7.0and a bimodal molecular weight distribution as determined by gelpermeation chromatography, and wherein the ethylene polymer extrusioncomposition has a melt index, I₂, of at least 1.0 g/10 minutes, (ii)melting and mixing the ethylene polymer composition to form at least oneuniform molten polymer stream, (iii) operating the extrusion line atline speeds greater than 152 meters/minute, (iii) extruding the moltenpolymer stream through a die to form a primary extrudate, and either(a)drawing down and cooling the extrudate to prepare the extruded profileof at least one layer of the ethylene polymer extrusion composition, or(b) drawing down the extrudate onto the substrate to thereby extrusioncoat the substrate with at least one layer of the ethylene polymerextrusion composition, or (c) drawing down and cooling the extrudateonto a take-off device to make the cast film with at least one layer ofthe ethylene polymer extrusion composition, and (vi) conveying orcollecting the profile, the extrusion coated substrate or the cast filmfor subsequent use.
 12. The process of claim 11, wherein the at leastone layer of step (iii)(a), (iii)(b) or (iii)(c) is a sealant layer,adhesive layer or abuse resistance layer.
 13. The process of claim 11,wherein the at least one layer of step (iii)(b) is an sealant layer. 14.An article comprising at least one layer of an ethylene polymerextrusion composition, wherein the extrusion composition comprises fromabout 75 to 95 percent, by weight of the total composition, of at leastone substantially linear ethylene/α-olefin polymer, wherein thesubstantially linear ethylene/α-olefin polymer is characterized ashaving a density in the range of 0.85 g/cc to 0.940 g/cc and is furthercharacterized as having(a) a melt flow ratio, I₁₀ /₂ ≧5.63 (b) amolecular weight distribution, M_(w) /M_(n), as determined by gelpermeation chromatography and defined by the equation:

    (M.sub.w /M.sub.n)≦(I.sub.10 /I.sub.2)-4.63,

(c) a gas extrusion rheology such that the critical shear rate at onsetof surface melt fracture for the substantially linear ethylene polymeris at least 50 percent greater than the critical shear rate at the onsetof surface melt fracture for a linear ethylene polymer, wherein thesubstantially linear ethylene/α-olefin polymer and the linear ethylenepolymer comprise the same comonomer or comonomers, the linear ethylenepolymer has an I₂, M_(w) /M_(n) and density within ten percent of thesubstantially linear ethylene polymer and wherein the respectivecritical shear rates of the substantially linear ethylene/α-olefinpolymer and the linear ethylene polymer are measured at the same melttemperature using a gas extrusion rheometer, and (d) a singledifferential scanning calorimetry. DSC, melting peak between-30 and 150°C., andfrom about 5 to 25 percent, by weight of the total composition,of at least one high pressure ethylene polymer characterized as having amelt index, I₂, less than 6.0 g/10 minutes, a density of at least 0.916g/cc, a melt strength of at least 9 cN as determined using a GottfertRheotens unit at 190° C., a M_(w) /M_(n) ratio of at least 7.0 and abimodal molecular weight distribution as determined by gel permeationchromatography, and wherein the ethylene polymer extrusion compositionhas a melt index, I₂, of at least 1.0 g/10 minutes.
 15. The article ofclaim 14, wherein the ethylene polymer composition is in the form of anextrusion profile, an extrusion coating into a substrate or an extrusioncast film.
 16. The article of claim 14, wherein the at least one layerof an ethylene polymer composition is an sealant layer, adhesive layeror abuse resistance layer.